1. Field of the Invention
The present invention relates to a fluorine-containing epoxy resin composition which is readily soluble in commonly used organic solvents and enables formation of a high quality coating film excellent in surface properties (hardness and smoothness), liquid repellent property, and adhesion property. The present invention also relates to a process of treating a surface of an object using said resin composition so as to form a surface excellent in surface properties (hardness and smoothness), adhesion property, and liquid repellent property on the object.
2. Related Background Art
It has been known that liquid repellent agents commonly used are stable thermally and chemically and are excellent in weatherability, water tightness, chemical resistance, solvent resistance, mold releasability, and liquid repellent property; however, they are not necessarily satisfactory in terms of hardness and adhesion to a member.
Such a liquid repellent agent has been used in a variety of industrial fields. For example, in the ink jet field, there has arisen an inconvenience that ink is accumulated on neighborhoods of discharging outlets provided in an ink jet head for discharging ink and the ink thus accumulated possibly causes deviation of the discharging direction of the ink and blocks the discharging outlets, and to cope with such an inconvenience, a liquid repellent agent has been applied on a surface provided with the discharging ports (the surface will be hereinafter occasionally be called a discharging outlet surface).
FIG. 14 is a schematic view showing one example of an ink jet head in which a discharging outlet surface is subjected to a liquid repellent finish using a liquid repellent agent. In FIG. 14, reference numeral 101 indicates a substrate for an ink jet head, which is formed of a material such as glass, aluminum or silicon. The substrate 101 is joined with a top plate 102 provided with grooves for forming liquid pathways 104. The liquid pathways 104 are formed of the grooves of the top plate 102 and the base plate 101. An energy generating element 103 for discharging ink is provided in each of the liquid pathways 104. A discharging outlet plate 107, which is provided with discharging outlets 108 each communicating with the liquid pathways 104 for discharging ink, is joined with a joined body of the substrate 101 and the top plate 102, to form an ink jet head. A liquid repellent layer 107a formed of a fluorine-based resin is provided on a surface having the discharging outlets 108 (hereinafter, referred to as a discharging outlet surface) of the discharging outlet plate 107. The liquid repellent layer 107a has a pattern as shown in FIG. 4 in which neighborhoods of the discharging ports have different liquid repellent properties than the remaining portion. As is well known, the configuration in which a liquid repellent area extends locally on neighborhoods of discharging outlets and a hydrophilic area 107' is formed around the liquid repellent area is effective in removal of ink adhering on the discharging outlet surface, as compared with a configuration in which the liquid repellent area extends over the entire discharging outlet surface.
That is, even in the case where a liquid repellent layer is provided on a discharging outlet surface of an ink jet head, if ink in mist adheres on the discharging outlet surface, it possibly remains thereon. In general, the ink remaining on the discharging outlet surface is removed by a wiping operation using a cleaning blade; however, if the ink remaining on the discharging outlet surface is thickened in viscosity, the removal of the ink using the cleaning blade becomes difficult. When the ink thickened in viscosity is located on neighborhoods of the discharging outlets, the ink accumulated thereon is liable to cause deviation of the discharging direction of ink and to block the discharging outlets. For this reason, the discharging outlet surface is so configured that it has a liquid repellent area around the discharging outlets and a hydrophilic area around the liquid repellent area for moving the ink remaining on the discharging outlet surface to the hydrophilic area. This makes it possible to at least reduce the possibility that the ink remains around the discharging outlets and to easily collect the ink in small droplets to the hydrophilic area, and hence to facilitate the removal of the ink using the cleaning blade.
In this way, the liquid repellent agent applied on a discharging outlet surface of an ink jet head needs to have a desired adhesion property, a desired rigidity (that is, hardness), and a desired wear resistance. From this viewpoint, a fluorine based resin used as the abovementioned liquid repellent agent does not adequately satisfy the needs regarding hardness and adhesion to a member. On the other hand, Japanese Patent Laid-open No. Hei 4-211959 discloses an ink jet head having a discharging outlet surface subjected to a liquid repellent finish using a liquid repellent agent composed of a polymer having a fluorine-containing heterocyclic structure at a main chain. The discharging outlet surface subjected to a liquid repellent finish using the above polymer is excellent in liquid repellent property and also relatively excellent in wear resistance. It is to be noted that the polymer having a fluorine-containing heterocyclic structure at a main chain is being practically used at present as a liquid repellent agent for a discharging outlet surface of an ink jet head.
It is understood from the above description that the polymer having a fluorine-containing heterocyclic structure at a main chain is effective as a liquid repellent agent used for subjecting a discharging outlet surface of an ink jet head to a liquid repellent finish.
The polymer, however, does not adequately satisfy the needs in all cases as will be described below.
That is, in recent years, a variety of cartridge type ink jet heads have been commercially available for eliminating the necessity of maintenance for the ink jet head. Such a cartridge type ink jet head (hereinafter, referred to as an ink jet head cartridge) adopts a configuration that the discharging outlet surface is protected with a discharging outlet surface protecting member such as a sealing tape or a cap. The discharging outlet protecting member is removed when the ink jet head cartridge is mounted on the ink jet system. Accordingly, for an ink jet head cartridge of a type being exchanged in accordance with the color and physical property of printing ink used, the exchanging operation of the ink jet head cartridge is conducted with the discharging outlet surface exposed. Upon this exchanging operation, the discharging outlet surface of the ink jet head cartridge is often brought in contact with the user's finger, the ink jet system and/or a head cartridge storage vessel. In the case where the discharging outlet surface of such an ink jet head cartridge is provided with a liquid repellent layer formed of a liquid repellent agent composed of the polymer having a fluorine-containing heterocyclic structure at a main chain, the liquid repellent layer is relatively excellent in wear resistance in the conventional service; however, since liquid repellent layer is formed of the polymer having a low hardness, it withstands the friction due to the wiping operation but it is possibly scratched when being brought in contact with the above-mentioned obstacles. If the liquid repellent layer is not directly scratched, there is a possibility that contaminants and the like adhere on the discharging outlet surface, and consequently the liquid repellent layer may be damaged when the contaminants adhering on the discharging outlet surface are pressed on the liquid repellent layer by the cleaning blade upon wiping operation.
On the other hand, in recent years, there has been proposed an ink jet system for conducting precise printing using ink in a relatively small droplet so as to further improve the quality of a printing image. In such an improved ink jet system using ink in a relatively small droplet, the distance between the discharging outlet surface and the recording medium such as a paper sheet is made very narrow for increasing the shooting accuracy. In the case where the distance between the discharging outlet surface and the recording medium is narrow, if there is a slight failure in carrying the recording medium, the discharging outlet surface may be rubbed with the recording medium, thereby damaging the discharging outlet surface. From this viewpoint, the discharging outlet surface of the above-mentioned ink jet system needs to be provided with a liquid repellent layer formed of a liquid repellent agent having such a high hardness that the liquid repellent layer is not damaged even if it is rubbed with a recording medium.
However, most of the fluorine based resins commonly used for the liquid repellent agent are relatively low in hardness.
Incidentally, a liquid repellent layer having a large thickness is advantageous in that when the liquid repellent layer is damaged, it has a non-damaged portion under the damaged surface portion, so that it is possible to prevent the deviation of the discharging direction of the ink. However, since the liquid repellent agent composed of a polymer having a fluorine-containing heterocyclic structure at a main chain is relatively low in adhesion property, the formation of a very thick liquid repellent layer causes a problem that the liquid repellent layer peels off. Accordingly, the liquid repellent agent used for forming a liquid repellent layer on a discharging outlet surface of an ink jet head is required to have a characteristic capable of suitably controlling the film thickness as well as an excellent film formability.
In this way, the conventional liquid repellent agent cannot make compatible the hardness with the liquid repellent property at a high level, and cannot adequately satisfy the above-mentioned requirements.
European Patent Laid-open No. 631869 discloses a process of imparting a liquid repellent function on a discharging outlet surface locally at neighborhoods of discharging outlets. This process is carried out by a manner of forming a liquid repellent film over the entire discharging outlet surface using a solvent-drying type liquid repellent agent, and partially cutting off the liquid repellent film on the discharging outlet surface by way of irradiation of an excimer laser beam, thereby forming a liquid repellent pattern in which a liquid repellent area is locally formed only on neighborhoods of the discharging outlets and a hydrophilic area is formed around the liquid repellent area. However, since a polymer used as the liquid repellent agent has a fluorine-containing heterocyclic structure at a main chain and is low in energy absorbing efficiency for excimer laser, it has a difficulty in formation of a fine patterning. On the other hand, Japanese Patent Laid-open No. Hei 5-124199 discloses a process in which a photosensitive resin having a liquid repellent property is formed as a liquid repellent agent on a discharging outlet surface, and is patterned using photolithography so that a liquid repellent function is imparted on the discharging outlet surface locally at neighborhoods of discharging outlets. This process is advantageous in that a fine local liquid repellent pattern can be formed, and that even when the discharging outlet surface is subjected to a liquid repellent finish after formation of discharging outlets, liquid repellent agent does not remain in the discharging outlets.
As for the known photosensitive resins having liquid repellent properties, including the liquid repellent agent (that is, photosensitive resin) described in Japanese Patent Laid-open Hei 5-124199, if they are excellent in their initial liquid repellent properties, they cannot sufficiently keep the liquid repellent properties for a long period of time. The reason for this may be considered to be due to low hardness of the photosensitive resins as the liquid repellent agents. That is, an area formed of the photosensitive resin having a low hardness is gradually abraded with the repeated wiping operations using a cleaning blade for cleaning discharging outlets.
As described above, the conventional liquid repellent agents are not suitable for formation of a local area excellent in liquid repellent property, hardness (that is, wear resistance), and adhesion property. In view of the foregoing, it has been required to provide a liquid repellent agent for forming a film having a local repellent function and having excellent hardness (that is, wear resistance) and adhesion property, particularly, at neighborhoods of discharging outlets on a discharging outlet surface of an ink jet head